Modems are communication devices that employ digital modulation techniques to transmit binary data across analog channels. In order to ensure interoperability, modems often conform to international standards. Some examples are, but not limited to, the V.90 standard described in International Telecommunication Union (hereinafter ITU)-T Recommendation V. 90, 9/1998 and the G.Lite standard described in ITU-G Recommendation G.922.2, 6/1999. In a typical configuration as shown in FIG. 1, several modems, or a modem pool, in remote access service (hereinafter RAS) concentrator 106 and modem 102 together provide user computer 100 access to servers on Internet 110. Specifically, the first available modem of the modem pool in RAS concentrator 106 would terminate the incoming call from modem 102. After having established a connection, RAS concentrator 106 then directs upper layer traffic (such as Web browsing requests) to router 108 that in turn routes the traffic to appropriate destinations, such as web server 114.
A modem contains at least four functional blocks as shown in FIG. 2. Though one ordinarily skilled in the art can partition these blocks differently. First, modem control block 200 regulates the actions of digital signal processing (hereinafter DSP) block 202, interprets modem commands from a data terminal equipment (hereinafter DTE), performs error control and data compression functions and finally sends and receives data. Second, DSP block 202 handles signal processing functions, such as, but not limited to, modulation, demodulation, echo cancellation, signal equalization, etc. DSP block 202 is sometimes referred to as the modem data pump. Third, analog front end (hereinafter AFE) 204 performs both analog-to-digital and digital-to-analog conversions. AFE 204 is sometimes referred to as CODEC or COder/DECoder. Lastly, data access arrangement (hereinafter DAA) 206 interfaces the modem to the phone line. DAA 206 not only provides safety protection to end users, but also provides features including, without limitation, voltage isolation, caller identification signal detection, ring signal detection and on-hook and off-hook functionality.
Instead of implementing these functional blocks with dedicated hardware, modem manufacturers, in efforts to reduce cost and improve performance, have shifted towards software solutions that take advantage of inexpensive yet powerful and highly integrated processors. For example, rather than building the modem pool in RAS concentrator 106 with individual modem boards, the modem pool can be a collection of software modems, or soft modems, that operate on one or more processors on a single board. One prior art design approach for such a single board arrangement is to select an appropriate processor that is capable of satisfying the aggregated peak computation load of its supported soft modems. Thus, if a processor supports eight soft modems, the processor should have sufficient processing capacity to accommodate the eight soft modems simultaneously operating under peak computation load conditions. One such condition is caused by a “retrain”, which occurs when the quality of a connection does not allow reliable communications over the full bandwidth expected by modems. However, because soft modems do not always operate under these peak conditions, the mentioned prior art design approach squanders many processor cycles.
Therefore, an improved method and apparatus is needed to provide a cost-effective solution to further increase capacity of a soft modem pool.